Research On Fault Location Of Small Current Grounding System With Traveling Wave Based On HHT

Small current neutral grounding is widely used in middle-low voltage distributionnetwork of our country. The system could continue to run for some time when single-phaseearth fault occurs, which is the most advantage of small current grounding. However, it is stilllack of accurate fault location method due to the fault signal is weak, so the problem of faultlocation on small current grounding system has not been completely resolved so far. With thedevelopment of the power system and increasingly high requirements of power supplyreliability, the problem of fault location on small current grounding system is becoming moreprominent. Therefore, there is a pressing need to resolve it fundamentally.The transient characteristics of small current grounding system have been analyzed whensingle-phase earth fault occurs. This paper describes the characteristics of Hilbert-Huangtransform (HHT) in detail. A comparison of HHT and traditional method namely Fouriertransform and wavelet transform has been explored. Then HHT, combined with three-terminal traveling wave method, is applied to detect the arrival time of traveling wave, whichcan be used to calculate the fault distance.The HHT is introduced to accurately determine the arrival time of transient currenttravelling wave. And the phase-model transformation is used for decoupling. On this basis,Intrinsic Mode Function (IMF) and remainder can be obtained by Empirical ModeDecomposition. Hilbert transform is applied to get the time-frequency figure of the first IMF.The mutational site of the frequency on the figure is the arrival time of the wave head.In order to eliminate the influence of line sag and wave velocity on measurementaccuracy, traveling wave fault location based on three-terminal measurement is used in thispaper. This method ignored the impact of velocity and sag factor. The parameters required inthis method are straight-line distance. And the time be detected is the first moment of faulttravelling wave arrive the detection end. Energy of travelling wave attenuates slowly,amplitude is greater and easy to detect.Finally, the simulation model of small current grounding system is established byMATLAB. Based on this model, a large number of simulation experiments are conducted.The fault location results under the different fault distance, different traveling wave faultlocation method and different signal detection methods are compared. The results show thatthree-terminal traveling wave method based on HHT gives high locating accuracy. Therefore,it is an effective fault location method of small current grounding system.